Puberty was induced in 39 clinically prepuberal gilts (two groups of three sub-groups each) by parallel but locally separated application of 500 IU PMSG ("Maretropin") and 250 IU HCG ("Gonadex"), with the view to testing ways to synchronise ovulation. Seventy-two hours were allowed to elapse, before 24 animals received another application of 500 IU HCG and 15 animals 250 IU HCG. The animals were slaughtered in consecutive groups of study ovulation and histolotically examined to disclose endometrial processes. Ovulations were found to be well synchronised in the recipients of a second injection of 500 IU HCG. Only sub-threshold effects with no synchronised ovulation were recorded from the animals that had received a second dose of 250 IU HCG. A second injection of 500 IU HCG should be given not until something between 78 and 82 hours after puberty induction for optimum follicle maturation and adequate proliferation of the endometrium.